In a vehicle, in order to realize more comfortable traveling and promote fuel saving, electronic control of in-vehicle devices has been progressed. The electronic control is performed by an electronic control unit (ECU: Electronic Control Unit) equipped with an information-processing device such as a microcomputer, but an amount of processes to be performed by one electronic control device is increased due to diversification and high-functionality in the electronic control, which results in tendency of increasing a process load of the microcomputer. It is considered to mount such a high-function microcomputer that can handle a peak of process load beforehand, but it causes a cost increase.
Thus, focusing attention on that a plurality of microcomputers are mounted in some electronic control devices, it is considered to distribute a load between microcomputers. Such a load distribution may be used in a networked PC or server (for example, refer to Patent Document 1). Disclosed in Patent Document 1 is a distribution process management system in which, in a state where calculators of substantially the same processing performance are connected to a network, each calculator records a load applied thereto on a common storage medium connected to each calculator. Each calculator finds a calculator being given a small load at a present time, and requests the calculator to execute a process.
However, because a plurality of microcomputers mounted in an electronic control device have a minimum necessary processing capacity in order to suppress a cost, it is difficult to use a simple load distribution such as disclosed in Patent Document 1. In addition, in many cases, a plurality of microcomputers mounted in one electronic control device have nonuniform processing capacities. Due to this, if, for example, a processing capacity of a microcomputer A is smaller than that of a microcomputer B, there may be a case where processing by the microcomputer B is faster than when the microcomputer A handles the process instead of the microcomputer B because the microcomputer A has a margin in a processing capacity. In addition, it is difficult in regards to not only cost but also size to mount a ROM of the same size in the microcomputer B so that the microcomputer A can handle the process of the microcomputer B instead.
In addition, if a microcomputer A and a microcomputer B having equal processing capacities are mounted in an electronic control device, a cost increase is caused as is the same as the above-mentioned case where a single high-performance microcomputer is mounted even if it is capable of performing a load distribution.
In the meantime, in a case of a vehicle, it is general that a high-performance side microcomputer performs a control process. When a processing load to the microcomputer for controlling becomes high, task omission may happen gradually, but the task omission happens from tasks giving small influence to traveling, and there is no situation where traveling becomes difficult. However, it is not preferable to cause any abnormality to occur in the microcomputer for controlling or in an execution of the tasks. Thus, the other microcomputer may be designed to monitor the microcomputer for controlling. The microcomputer for monitoring monitors a process load of the microcomputer for controlling, and if it is determined that a high-load level is reached, there may be a case where the microcomputer for controlling is reset and reactivated. In this case, the microcomputer for controlling returns (reactivates) extremely faster than a general-purpose PC or the like, but it is not preferable that a control is not performed even in a short time period.
Patent Document 1: Japanese Laid-Open Patent Application No. H09-319720